Time-variable strain and stress rates induced by Holocene glacial isostatic adjustment in continental interiors

In continental interiors, tectonically-driven deformation rates are low, often to the point where they are undetectable with modern geodesy. However, a range of non-tectonic surface processes, particularly relating to hydrological, cryospheric, and sedimentological mass changes, can produce strain-rates which on geologically-short timescales are substantially greater than those produced by tectonics. Here, we illustrate the problem that such transient strain rates may pose in low-strain environments by considering the impact that the growth and decay of the Fennoscandian and Laurentian ice sheets over the Holocene had on Europe and North America respectively. Induced deformation extended far beyond the periphery of the ice sheets, with the potential to impact on seismicity rates thousands of kilometres south of the maximum ice extent. We consider how the modelled non-tectonic deformation would have interacted with several known active fault systems, including the European Cenozoic Rift System and the New Madrid fault system. In low strain continental interiors, seismic hazard assessment – crucial for the long-term planning of critical infrastructure, including nuclear waste disposal – is often dependent on sparse information from observational and historical seismicity, and from paleoseismological studies of surface fault systems. We recommend that for a more complete seismic hazard assessment, the impact of non-tectonic transients should be considered – both in the context of the role such transients may have played in recent seismicity, and the role they may play in seismicity to come. Whilst such consideration has previously been given to the direct impact on glacial loading in areas directly glaciated, we show that it should also be considered much more broadly.